Method of extracting uranium from bituminous shales and shale culm containing uranium



by weight.

'terial to ash, not necessary to grind the raw material to a Patented May 20, 1952 UNITED STATES PATENT OFFICE 2,597,504 METHQD OF'EXTR'ACTING URANIUM FROM BITUMINOUS SHALES "AND SHAL'E CUL'M CONTAINING URANIUM No Drawing. Application December 3, 1948, Serial No. 63,441. In Sweden December 4, 1-947 4 Claims.

organic matters the percentage of uranium is essentially higher than in the bituminous shale 'per's'e. For instance the percentage of uranium 'in' bituminous shales can amount 1:00.02 to 0.03

'by'weight while the percentage of uranium in the shale culm may be for instance 0.4 to 0.5% As the percentage of combustible organic matter in the shale culm is rather high the ash from such culm can contain up to 2 to 255%by weight of uranium.

It has already been proposed to leach ashes from shale culm with a solution of sodium carbonate in order to extract uranium, radiumand other valuable constituents. The result was, however, not satisfactory :as only about to A of the total percentage 'of uranium in the ash could be recovered in such manner. In leaching ashes from bituminous shale containing uranium with ya solution of sodium carbonate the result will likewise be unsat-isfactory as the chief :part of the uranium will remain in an insoluble state in the ash.

This invention relates to an improved method of extracting uranium from bituminous shales and shale culm containing uranium by means of Ia solution of alkali carbonate andconsists chiefly in this that the shale or the shale culm is leached in its natural state, i. e. without -a preceding coking or combustion of the raw ma- In I such leaching operation it is fine powder in as much as -a satisfactory extraction of the uranium can be performed, if the raw material is crushed to a grain size of about 0.25 ,to0.15 mm.

the leaching of the raw material in its natural state with a solution of alkali carbonate the astonishing effect is attained that the yield of uranium will :be essentially higher than in leaching ashes from said raw material though the quantity of raw material in the former case is essentially larger than in the latter case, for instance in leaching shale culm in natural state about 4 to 5 times larger than in leaching ashes from the-culm.

It has been found that the extraction of the uranium is facilitated and improved if the raw materiar before 01' after its mixing with the 's'ol iti'on' of alkali carbonate is subjectedto the oxidizingyaction of air or a gas "rich in oxygen 'at aitemperature slightly above room tempera- 2 ture, for instance in such manner, that :air or a gas rich in oxygen .is blown through a sludge of the raw material and a solution of an alkali carbonate, or in such manner, that the raw material is moistened with a solution of alkali carbonate of a suitableconcentration whereupon air or gas rich in oxygen is conducted through the moist though stillporous mass.

In such oxidizing step .a maximum "effect is obtained by using air 'or a gas rich in oxygen at a temperature of about to C. It is essential that the oxidizing is carried out at a moderate temperature in as much "as otherwise the organic substance in the raw material also would be oxidized to a considerable extent and be dissolved in the alkalicarbonate solution.

In leaching the raw material without a preceding oxidizing I have found that an increase of the leaching temperature does not essentially increase the yield of uranium until the boiling I point of the solution is reached, but at the In order to obtain a good yield a rather concentrated solution of alkali carbonate should be used. When bituminous shales containing sul- "phuric acid either as free acid or as sulphates are treated the alkali carbonate is partly converted into alkali sulphate. In the oxidizing step also the sulphides possibly present in the raw material are oxidized to S02 and possibly also to S03 which also convert a part of the alkali carbonate to alkali su-lphite and alkali sulphate -respectively. The solution separated from the leached raw material can preferably be used repeatedly in leaching fresh quantities of the raw material in which case, however, also fresh quantitles of alkali carbonate should be added to the solution so .as to maintain its content of alkali carbonate substantially constant.

By using the leaching solution repeatedly its content of uraniumi'ssuccessively increased. When the uraniumhas reached a suitabl constance by neutralizing the alkali -=carbonatewith sulphuric acid, whereby the uranium is caused to precipitate as alkali diuranate. The solution separated from the precipitate and containing chiefly alkali sulphite and alkali sulphate may be evaporated and the solid salts recovered be converted in well-known manner into alkali carbonate for renewed use in the process.

As alkali carbonate preferably sodium carbonate, NazCoa, is used but also potassium carbonate or ammonium carbonate or bicarbonates of the alkalies may be used. Sodium carbonate is, of course, to be preferred as it is the cheapest alkali carbonate. When not otherwise stated I use in the specification and the claims the expression alkali carbonate in a sense including the normal alkali carbonate, M2003 as well as the alkali bicarbonate, MHCOa."

Instead of oxidizing the raw material mixed with the alkali carbonate it is possible to oxidize the raw material before the alkali carbonate solution is added.

I'have found that in carrying out the process with some bituminous shales containing uranium the yield of uranium'will be low even if the raw material is oxidized as above described and then extracted with a solution of alkali carbonate at the boiling temperature of the latter. In such case the yield can be essentially improved by performing the leaching operation in a closed apparatus at an over-pressure and at a correspondingly high temperature above 100 C. In such case it is not always necessary to oxidize the raw material. It is also to be noted that in a such case good results are obtained not only when using a solution of normal alkali carbonate as leaching agent but also when a solution of a1- kali bicarbonate or a solution containing a mixture of alkali carbonate and alkali bicarbonate is used. When alkali bicarbonate is used as leaching agent carbon dioxide is developed during the high extraction temperature used, which causes an elevation of the pressure in the closed apparatus. When using temperatures above 200 C. in the extraction process also the silicic acid of the raw material is dissolved by the normal alkali carbonate to a considerable extent. Said inconveniences are, however, substantially avoided by using as leaching agent a solution containing alkali bicarbonate up to 50% of the total quantity of alkali carbonate. I have found that in such case the development of carbon dioxide also at high temperatures as well as the dissolving of silicic acid are essentially reduced. When leaching the raw material with a solution containing normal alkali carbonate as well as alkali bicarbonate at high pressures and high temperatures the yield of uranium is also improved in comparison with a leaching under the same conditions with a solution containing normal alkali carbonate alone. 1 v

Examples I. 1 kg. of bituminous shale containing-uranium and ground to such grain size that99% thereof passed through. a sieve with 25' mm.

meshes was mixed with 1 l. of a solution of sodium carbonate whereupon oxygen-was supplied to the mixture at a temperature 'of about 25C; When about 1.5 1. oxygen had been absorbed the solid matters were separated by filtering and washing. The clear solution obtained contained .24 g. of uranium-oxide (U308) 1 which could be recovered as sodium uranateby neutralizing with sulphuric acid. .g';

II. .1 kg. of the same bituminous .Shale;- asin Example I was mixedwith 1 l. of a 10%-"solution 4 of sodium carbonate whereupon the sludge was heated to the boiling point while stirring during about 1 hour. The solution separated from the sludge contained .24 g. of uranium oxide (U308) III. 1 kg. of the same bituminous shale as in Example I was mixed with 1 l. of a 10% solution of sodium carbonate whereupon the sludge was oxidized as in Example I and then boiled while stirring during 30 minutes. The solution separated from the sludge contained .27 g. of U303.

IV. 1 kg. of the same shale as in Example I was mixed with 2 l. of a 10% solution of sodium carbonate whereupon air was blown through the sludge while stirring during 1% to 2 hours. The solution separated from the sludge contained .245 of U308.

V. 1 kg. of another sample of bituminous shale ground to the same fineness as in Example I was boiled while stirring together with 1 l. of a 10% solution of sodium carbonate. The clear solution separated from the sludge contained .13 g. of U308.

VI. .4 kg. of the same shale as in Example V was mixed with a solution of 8 g. of NaOH and 10 g. of NazCOa in about 70 cc. of water. 'The moist mass was placed in a U-shaped tube through which oxygen was conducted. The mass was then mixed with 400 cc. of water and. sodium carbonate was added until a concentration of 10%. The mixture was then heated to the boiling point while stirring in about 1 hour. The solution separated contained .17 g. of U308.

VII. .5 kg. of a shale culm ground to such grain size-that 99% passed through a sieve with .15 mm. meshes was mixed with 1 l. of a 10% 'solution of sodium carbonate whereupon the mixture was heated to the boiling point while stirring during about 2 hours. The solution separated from the sludge contained 1.725 g. of U308, corresponding to an output of about 78%. VIII. .5 kg. of the same shale culm as in Example VII was mixed with. 1 kg. of a 10% solution of sodium carbonate whereupon the mixture was first'oxidized by means of oxygen at 30 C. and then heated to the boiling point while stirring during 2 hours. The solution separated from the sludge contained 1.962 g. of U308, corresponding to an output about IX. 1 kg. of a bituminous shale ground to such grain size that 90% thereof were less than 0.15 mm. was mixed with 1.4 l. of a 10% solution heated to 50 C. and then shaken in an atmosphere of oxygen until 2 l. of the oxygen had been I absorbed. The sludge was then heated to the boiling point of the solution while stirring in about 2 hours. The solution contained .08 g. of U303.-

X. This test was carried out with the same shale as in Example IX but at an overpressure and a correspondingly elevated temperature. 1 kg. of the shale was mixed with 1.4 l. of a 10% solution of sodium carbonate whereupon the sludge was heated to a temperature of about C. at an overpressure of 5.5 atmospheres during 2 hours while stirring. After filtering and washing the clear solution obtained contained .18 g. of uranium oxide (U308) I claim:.

1. Method of extracting uranium from-,bitu

minous shale containing uranium, whicjhlcomprises preparing a suspension of the shale in its natural chemical state in a solution ofialkali carbonateyblowlnga gas containing free-oxygen 5 through said suspension and then separating the extract from the solid matters.

'2. Method of extracting uranium from bituminous shale containing uranium, which comprises preparing a suspension of the shale in its natural chemical state in a solution of alkali carbonate, blowing a gas containing free oxygen through said suspension while maintaining the suspension at a temperature of 25' to 33 C., and then separating the extract fromthe solid matters.

3. Method of extracting uranium from bituminous shale containing uranium, which comprises preparing a suspension of the shale in its natural chemical state in a solution of alkali carbonate, blowing a gas containingfree oxygen through said suspension, then :heating the suspension to a temperature of at least 100 0., and finally separating the solution from the solid matters.

4. Method of extracting uranium from bituminous shale containing uranium, which comprises preparing a suspension of the shale in 7 titles of the raw material.

MARKUS LARSSON.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 1,429,550 'Vogt Sept. 19, 1922 1,438,357 Bleecker Dec. 12, 1922 Gibbs Apr. 30, 1935 I OTHER REFERENCES Mellor, Inorganic and Theoretical Chemistry, volume 12, page 8 (1932). Published by Longmans, Green and Company, London. 

1. METHOD OF EXTRACTING URANIUM FROM BITUMINOUS SHALE CONTAINING URANIUM, WHICH COMPRISES PREPARING A SUSPENSION OF THE SHALE IN ITS NATURAL CHEMICAL STATE IN A SOLUTION OF ALKALI CARBONATE, BLOWING A GAS CONTAINING FREE OXYGEN THROUGH SAID SUSPENSION AND THEN SEPARATING THE EXTRACT FROM THE SOLID MATTERS. 